Steelmaking

Trial production of free cutting gear steel by converter process under semisteel steelmaking condition

2012, 28(1): 1-4,10. doi:

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In view of the composition characteristics and quality requirement of free cutting gear steel 20CrMnTiH（FQ）and in combination with the production conditions of equipment and process in Panzhihua Steel, technologies of free cutting gear steel producing have been studied. With these technologies such as sulfur content increasing in semisteel, endpoint control of converter, proper deoxidation process, reasonable aluminium control, secondary refining process, modification of inclusions type A with segmented calcium treatment, sulfur content increasing after RH refining process, as well as optimization of parameters in continuous casting process, 20CrMnTiH（FQ）can be produced steadily with semisteel making conditions in the process of Convert Steelmaking→LF→RH→Continuous Casting. Results of industrial production indicate that the compositions of 20CrMnTiH（FQ）steel can be confined in a narrow range, and sulfur in steel controlled steadily as well. Moreover good surface and internal quality of continuous casting billet can be produced and w（T.O）is governed in the range of （11～18）×10^-6with the average value of 14.7×10^-6. Nonmetal inclusion in steel and performance index of rolled bars can meet the requirements of consumers.

Analysis of CaS inclusions in calcium treated drilling steel

2012, 28(1): 5-7,19. doi:

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The character of inclusions in calcium treated 37CrMnMo was analyzed. Fine spheroidzed CaO-Al₂O₃-CaS complex inclusion was formed after proper calcium treating. However some discontinuous granular CaS inclusions were found in the steel. The effect of Al, Ca, O, S on the forming of CaS was discussed through data statistics and thermodynamic. Finally, effective measurement was brought forward.

Application of spectral inclusion analysis technology in IF steel

2012, 28(1): 8-10. doi:

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The technology of spectral inclusion analysis by a PDA spectroscope is introduced. The Al₂O₃ inclusion contents in the qualified heats as well as inclusion caused rejected heats of liquid steel used for cold rolled IF steel sheets purposes are analyzed at the RH end point in the process of refining and at the intermediate phase of tundish casting by means of this technology. Preliminary inclusion control tech index for IF steel sheet in the process of refining are put forward as follows: RH endpoint inclusion quality fraction be controlled within the limit of less than 0.004 5 %and inclusion quality fraction in the tundish, in less than 0.003 0 %. Since application of the technology in the actual production practice of IF steel sheet in 2009 in combination of the other processes the rejected rate of the cold rolled IF steel sheets arising from inclusions have been dramatically reduced.

Effect of electromagnetic stirring in secondary cooling zone on quality of continuous casting slab of nonoriented silicon steel

2012, 28(1): 11-14,2. doi:

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The effect of electromagnetic stirring parameters in secondary cooling zone on equiaxial crystal rate, center segregation and white band of continuous casting slab of XG800WR nonoriented silicon steel was investigated. The results show that the equiaxial crystal rate of slab grows from 19.6 % to 26.5 % when stirring current varies from 0 A to 400 A. The equiaxial crystal rate of slab grows from 21.7 % to 26.1 % when stirring frequency increases from 0 Hz to 8 Hz. With stirring current increasing, the segregation degree of S, Si, Mn in slab center is firstly decreased and then increased. When stirring intensity is excessive the white band appears and in the area of the white band the negative segregation of Si, Mn and S occurs and the negative segregation index of S is the largest. All of the phenomena will consequently lead to an increase of positive segregation of S, Si and Mn in the center of slab. In a comprehensive consideration of increase of the equiaxial crystal rate, reduction of central segregation and avoidance of white band occurrence the 350 A/6 Hz is selected as the optimal electromagnetic stirring parameters.

Monitoring & analysis on mold cooling water temperature difference for bloom continuous casting

2012, 28(1): 15-19. doi:

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According to large quantities of measured data, the present paper discussed the relationship between the temperature difference of cooling water in the mold and the process parameters such as casting speed, superheat and mold water flow rate, and the multivariate statistical method was used to expound its quantitative law. Secondly, the functions of monitoring water temperature difference were illustrated mainly to guide the development and optimization in the cooling process. Finally, the mean filtering method was applied to the data acquisition so as to ensure the calculation accuracy and stability of dynamic thermal tracking model for casting bloom and practice demonstrates the necessity and effectiveness of the method.

Origin of corner crack of slab for automobile beam steel M510L and optimization of secondary cooling process

2012, 28(1): 20-24. doi:

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On the basis of analysis on the high temperature mechanics properties of the automobile beam steel M510L the secondary cooling process for
the No.2 Continuous Casting Machine of Ma’anshan Steel Co., Ltd.
has been optimized and therefore the high temperature ductility has been
improved. In the meanwhile every possible means has to be taken to keep away from the fragile sensitive zone. The corner quality of the slab
has been improved and the rate of corner trimming rate of steel M510L lowered to 15 % from original 95 % due to optimization of the
secondary cooling water supply as well as insurance of the accuracy of the arc for the segments and the accuracy of the roll gap control.

Research on mechanism of longitudinal surface crack formation of thin slab and mould taper

2012, 28(1): 25-28. doi:

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Mechanism of longitudinal surface crack formation of thin slab is discussed from the view of mechanics. The effect of control process of mould taper on longitudinal surface crack of thin slab is analyzed. Controlling measures on longitudinal surface crack are discussed in detail. The results show that local tensile stress concentration is one of main reasons to promote formation of longitudinal surface crack. Controlling measures on longitudinal surface crack include two ways. One is improving the growing uniformity of solidified shell. It can be carried out by optimizing continuous casting process. The other is promoting optimization of contact situation between mould and solidified shell and it can be assured by optimizing inner structure of mould and adjusting taper.

Reasons for formation of longitudinal crack of CSP slab and preventing measures

2012, 28(1): 29-32,3. doi:

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Longitudinal cracks on surface of thin slab are common defects in continuous casting of CSP.According to the formation mechanism of longitudinal cracks in continuous casting process of CSP slab，combining with site experience of WISCO production, this article analyses the reasons of formation and expansion of longitudinal cracks from composition of liquid steel，taper of mould，behavior of casting powder，second cooling condition，equipment accuracy and so on.The article puts forward the measures for effective control the longitudinal cracks of CSP slab.After tackling key measures，the modify ratio reduced from 3.22 % in December 2009 to 0.43 % in December 2010，and longitudinal cracks are effectively controlled.

Experimental study on environmentfriendly dephosphorization agent for  high phosphorus hot metal pretreatment

2012, 28(1): 33-36. doi:

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In order to develop high efficient and environmentfriendly dephosphorization agents, in this paper, the Factsage^TM was used to plot ternary phase diagram about Fe₃O₄-CaO-B₂O₃and Fe₃O₄-CaO-K₂O.
The mass fraction of B₂O₃system andK₂O system dephosphorization agents were determined by the ternary phase diagram. Then dephosphorization experiments were conducted in the laboratory. The experimental results of high phosphorus hot meal predephosphorization using B₂O₃ as a flux were compared with that using CaF₂ as a flux. The results show that, as a flux, B₂O₃ can replace completely CaF₂ to predephosphorize the high phosphorus hot metal. This dephosphorization
agent can remove phosphorus to below 0.1 %. In this case the ratio of w( B₂O₃ ) and w(CaO) is 0.16. When this dephosphorization agent is used to dephosphorize, there is good state of slag melting. At the same time no foaming slag appears. And its dephosphorization rate is the highest in all of dephosphorization agents. But K₂O system dephosphorization agent has unsatisfactory dephosphorization efficiency.

Water modeling study on auxiliary deslagging process by air blowing in hot metal tank

2012, 28(1): 37-39,5. doi:

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By way of water modeling the deslagging process with air blowing in the hot metal pot is investigated. In the meanwhile the effects of factors
such as the type of the air brick, fixing position and rate of blowing air flow on the results of deslagging by auxiliary air blowing are systematically studied. Results show that the double blowing process is better than the single one and the twin bubble brick is superior over the traditional single bubble brick and moreover the lower the bubbling element is fixed and the larger the spread area of the blown liquid level is, the better
the deslagging effects will be. Since the successful application of the experimental results in the onsite production the deslaging time is
reduced to about 6 minutes from the original 12 minutes and the hot metal deslagging rate is drastically improved and sulfur pickup rate in
the converter is effectively controlled within 0.005 %.

Analysis and optimization of V and Ti containing hot metal desulfurization process

2012, 28(1): 40-43. doi:

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In combination with the basic situation of vanadium and titanium containing hot metal desulphurization in a specific plant, the characteristics and the main problem of vanadium and titanium containing hot metal desulphurization process were analyzed. Through experiment research and field tracing, the physical and chemical properties of hot metal containing vanadium and titanium, hot metal temperature, the desulphurizing ability of desulfurizer, process operation and other factors affecting the desulphurization performance have been studied. And combined with field desulphurization production, the optimization of desulphurization process for the hot metal containing vanadium and titanium was carried out and good effect obtained accordingly.

Effect of oxygen content on cutting performance in sulfur free cutting steel

2012, 28(1): 44-47,6. doi:

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The present paper studies the effect of oxygen content on sulfide inclusions and cutting performance of the sulfur free cutting steel. The results show that cutting performance of the steel tends to be better and better with increase of oxygen content within a certain range because massive spindle (Mn, Fe) (S, O) complex inclusions can be formed in steel when oxygen content is high. In the cutting process this kind of sulfides can cut off the continuity of matrix and form a protective film on the cutter surface to reduce tool wear. The results of cutting experiment show that the cutting performance is better than steel 45 when oxygen content is 0.014 % and ideal cutting performance can be obtained.

Influence of calcium treatment on total oxygen content in non-oriented silicon steel

2012, 28(1): 48-51. doi:

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The SiCa cladded wire is fed into the hot metal after RH vacuum treatment. The effect of Ca treatment on the total oxygen content of the nonoriented silicon steel is investigated by comparison of variation of T.O and N as well as change of sizes and quantity of inclusions before and after Ca feeding. Thermal dynamical calculation shows that in the nonoriented silicon steel the total oxygen in steel can basically represent the total quantity of the oxide inclusions in the steel due to higher Al and low free oxygen content in the steel. The total oxygen content in steel can be drastically reduced through Ca treatment mainly because the inclusions modified by Ca treatment will grow larger and their concentration is accordingly reduced. Thereby those relatively larger inclusions will more easily float up.

Study and application of flow field of asymmetrical 5 strand tundish

2012, 28(1): 52-56. doi:

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By water modeling the optimal plan for baffle of the asymmetrical five strand tundish has been determined and law of distribution of inner flow field and temperature field of the tundish studied by application of numerical simulation. Results show that since optimization the flow field and temperature field of the tundish tend to be consistent and uniform and the internal structure inside each strand is of high uniformity and the internal quality of the bloom is excellent and they can basically meet the product quality requirements and production demand.

Optimization of secondary cooling scheme for 40Cr alloy structural steel in billet continuous casting

2012, 28(1): 57-61. doi:

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The solidification and heat transfer model for billet continuous casting is established and the model accuracy validated by the infrared temperature measurement method. By model calculation the problems currently existing in the secondary cooling schedule for the 40 Cr alloy steel is analyzed and at the same time the problems of over strong cooling intensity at the food roll segment, higher temperature recovery existing in the No.1 zone of the secondary cooling segment, excessive secondary cooling water volume and relatively lower surface temperature of the billet at the straightening zone are found out. A reasonable set of K value combination ( water volume adjustment parameters) is fed into the model computer after optimization and then a more reasonable K value combination namely K₀=0.3，K₁=1.0，K₂=0.9，K₃=0.7 is obtained. At the same time the secondary cooling water rate is lowered, the straightening temperature of the billet raised, the brittle temperature zone avoided and thus the rate of crack occurrence of the billet reduced. It can be used as guidance for the process optimization of the billet continuous casting.

Influence of copper plate thickness on thermomechanical behavior of slab mold

2012, 28(1): 62-65. doi:

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In connection with the practical conditions of one caster in a specific plant a threedimensional thermal elasticplastic finite element model is established and distributions of temperature, deformation rate and equivalent stressstrain for copper plates with different thickness are obtained. All those parameters are used to guide the design of mold in the Steelmaking Co., Ltd. of Hebei Puyang Iron & Steel Corporation. Results show that the thicker the copper plate is, the higher the temperature will be at the hot surface, and the less the equivalent stress is, the larger the deformation rate will become. Every 5 mm increase in the thickness of the copper plate will inevitably lead to about 30 ℃ temperature increase in the highest hot surface and about 7.5 MPa reduction of the maximum equivalent stress at the hot surface and about 0.05 mm increase of the maximum deformation rate at the hot surface. Thinner copper plate is more helpful for reduction of the hot deformation of the copper plate in the process of casting.

RH process design under low rail surface elevation condition

2012, 28(1): 66-69. doi:

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The present paper introduces the RH process design under low rail surface elevation condition and describes in detail the design of lowering the top elevation of top oxygen blowing gun and the elevation of ferroalloy feeding system. This process design has been successfully applied to a number of construction project such as 100 t RH of Lianyuan Iron & Steel、150 t RH of Xiangtan Iron & Steel、120 t RH of Jiuquan Iron & Steel and 120 t RH of Liuzhou Iron & Steel. It is of great significance for improvement in the design and process level of the similar equipments in China.

Analysis on failure of mold copper plate of continuous caster and counter measures

2012, 28(1): 70-73,7. doi:

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In order to increase the service life of casting molds，some improving measures are put forward. The failure reasons of copper plate and its surface coatings are analyzed. In addition，the design of the casting mold，the selection of materials and surface hardening technology are studied. Furthermore，by means of comparison of Ag-Cu and Cr-Zr-Cu metallographic structure photos，Cr enriched metal compounds segregated from the interface of the copper crystal cells is primary cause to the thermal cracks of the Cr-Zr-Cu mold plate. The internal stress distributions of alloy electroplated layers，thermal spray coatings and nanoceramic composite coatings are researched，and production technology of the copper plate coating was optimized. A new coating layer with low stress is developed independently without any organic additives，which used in some steelmaking works and scratch resistance and thermal crack resistance of casting mold are very satisfactory in the actual application of the technology.

Status of research on mold flux for high aluminum steel

2012, 28(1): 74-78. doi:

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In light of the characteristics that the mold flux Al₂O₃ content is enormously increase in the process of continuously casting the high Al steel the present paper introduces the origin of Al₂O₃ in the mold flux and its influence on the properties as well as absorption of Al₂O₃ by the mold flux. By way of summarizing the status quo of research on the high Al containing mold flux at home and abroad in the recent years it's found out that at present time most of the mold flux are mainly composed of low Al₂O₃ and high SiO₂constituents and a large quantity of slag rim are formed in process of usage, thus resulting in occurrence of deeper surface depression of the slab. On the contrary high Al₂O₃ and low SiO₂ constituents can help keep chemical compositions and properties of the mold flux intact in continuously casting the high Al steel and therefore they can be used in the research and development of the mold flux for high Al steel.

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